Occlusive disease of an artery, frequently the result of atherosclerosis, is sometimes treated by the surgical procedure of endarterectomy. In an endarterectomy, an incision is made in the artery at the site of the occlusion. The thickened intima of the artery along with any other components of the lesion such as atherosclerotic plaque or thrombus, is then removed. In order to perform this procedure, the artery must necessarily be occluded above and below the area operated upon, typically with a pair of clamps. This means that there is no blood flow through the artery during the operation, but collateral circulation is usually adequate to support the metabolism of the area fed by the artery for a short period.
One of the most common sites of occlusive arterial disease is the internal carotid artery, usually at its origin at the bifurcation of the common carotid. Endarterectomy is sometimes the treatment of choice for these cases. Clamping of the carotid artery as described above, however, necessarily means that cerebral blood flow is compromised during the procedure. The situation can be evaluated during the operation by measuring the pressure in the internal carotid artery after application of occluding vascular clamps to the common carotid artery and the external carotid artery. This measurement of carotid "stump pressure" is indicative of the adequacy of collateral circulation to the brain. If it is below 50 mmHg, brain perfusion may not be adequate, thus necessitating the use of a temporary shunt during the procedure. Some surgeons even choose to routinely use such a shunt during all carotid endarterectomies without regard to measured "stump pressure."
An arterial shunt is basically a pliable tube which provides a pathway through which blood may flow in order to bypass the operative site. A conventional shunt is formed with two limb sections joined together with a single trunk section extending from the point where the two limbs meet. A continuous blood flow lumen exists in all three sections. One limb is inserted into the artery through the surgical incision on one side of the lesion while the other limb is inserted on the opposite side of the lesion. Blood then flows from one limb to the other, thus bypassing the operative site. The trunk section is normally connected to a stopcock which allows access to the circulation for pressure monitoring or drug administration, as well as allowing air in the shunt to be purged. The trunk section also contains two auxiliary lumena separate from the blood flow lumen. Each auxiliary lumen extends into a selective one of the limb sections. At the distal end of each limb, an annular balloon is positioned which surrounds the shunt tubing but does not obstruct the blood flow conduit. Each annular balloon is connected to an auxiliary lumen from which the balloon may be inflated, typically with saline. Thus, a tight seal is formed within the artery to provide an effective bypass and to keep the operative field free of blood. Alternatively, the auxiliary lumena and balloon arrangement may be eliminated and replaced by simply tying a suture around the artery to secure the limb section within on each side of the incision.
A major complication which can arise while performing a shunt endarterectomy is for the shunt to become occluded either by a thrombus or dislodged plaque. This can occur initially as the shunt is inserted into the artery or at any time during the procedure. This is, of course, a potentially disastrous complication unless corrective action is taken quickly. However, in heretofore conventional shunts it has been difficult to tell whether blood is flowing adequately therethrough.